<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            width: 200px;
            height: 200px;
        }
        .a{
            background-color: blue;
            position: relative;
            top: 100px;
            left: 100px;

        }
        .s{
            background-color: blueviolet;
            position: relative;
            /*层级*/
            z-index: 1;
            /*z-index:值越大，层级越大，在上面显示*/
        }
    </style>
</head>
<body>
    <div class="a"></div>
    <div class="s"></div>
</body>
</html>